Comparison of Satellite Microwave and Visual Shipborne Data on Sea Ice Concentration

In this paper we compare the sea ice concentration data obtained by satellite microwave radiometry using the NASA Team, ASI, and VASIA2 algorithms and by special visual ship observations. A database of visual observations of the sea ice concentration obtained during 15 expeditions in the Arctic was used. The comparison for various concentration gradations (very open, open, close, very close, and compact ice) was carried out separately for summer and winter periods. On average, during the summer period, the NASA Team algorithm underestimates the sea ice concentration by 1 point, while the ASI and VASIA2 algorithms underestimate by 0.5 points when compared to ship observations. All three algorithms overestimate the total concentration in the zones of very open ice and underestimate it in the zones of close, very close, and compact ice. The maximal average errors are characteristic of open ice that is most often observed in ice edge zones. In winter, the average error for all algorithms is no more than 1 point when compared with ship observations. However, in very open and close, the average error in winter is significantly higher than that in summer. To assess the effect of melting processes on the concentration values obtained by satellite microwave radiometry, we used ship data on ice melt stage. The average error at the maximal area of ​​melt ponds on the ice surface reaches –2.9 points for the NASA Team algorithm, –2.8 points for the ASI algorithm, and –5.0 points for the VASIA2 algorithm. The results will be useful for determining the extent of ice-cover degradation in the Arctic Ocean observed in recent years.